The increasing use of multilevel metallization in the fabrication of very large scale integrated circuits (VLSI), combined with the desire to reduce the geometries in such circuits, makes it essential that etching of aluminum metallization be anisotropic. Therefore, to be commercially attractive, any etchant gas mixture or process manipulation developed to alleviate a problem or problems commonly associated with the plasma etching of aluminum metallization must still possess the capacity to perform an efficient, anisotropic etch.
One such problem is the contamination caused by material or gases from the walls of the plasma reaction chamber. For aluminum etching, the plasma reaction chamber is generally made of aluminum to prevent cross-contamination. The chamber walls are conventionally protected against etching by a thick plasma-sprayed coating of aluminum oxide. This oxide coating, however, is porous and can absorb gases and water vapor from the reaction chamber, which are a source of contamination of the substrate being etched. In addition, since the aluminum oxide layer is generally rough, it is often difficult to remove material deposited thereon during an etching procedure which may be a source of contamination for subsequent procedures. These contamination problems affect both etch reproducibility and efficiency.